Arsenal undone by red Van man - Robin van Persie

Arsene Wenger will have to change his belief that his former captain still has the club in his heart. Robin van Persie refrained from celebrating his two previous goals against Arsenal last season but he reacted wildly to his first-half headed goal here. He raced towards the corner-flag, sliding on his knees into the embrace of Wayne Rooney and further into the enmity of the visiting fans.

Van Persie's jubilant reaction was partly a response to the venomous chants his former admirers had been singing about him. Their resentment over his 2012 departure, after Wenger had backed the striker through injuries and one off-field difficulty, has not abated. So they taunted Van Persie from the start, reminding him they were "eight points clear, Robin, eight points clear" and that was the cleanest chant. Not for long.

By full-time, Arsenal were only five ahead of fifth-placed United, whose self-belief will have been immeasurably lifted by the result, by their tempo in the first half and resilience in the second. Doubt seemed to have taken up permanent residence at Old Trafford since Sir Alex Ferguson left the dug-out for a smart seat in the stands. Many observers have expressed reservations about his successor, David Moyes, so this was a hugely important result for him. It stilled some of the squalls around him. It also ensured United still retain an interest in the Premier League race, which became even more of a fascinating, unpredictable chase over the weekend.

Yet the game is about such fine lines. Having been forced into swapping Nemanja Vidic for Tom Cleverley at half-time following the captain's head injury that saw him taken to hospital, Moyes' substitutions were largely defensive, stiffening midfield with Ryan Giggs replacing Shinji Kagawa and Marouane Fellaini coming on for Van Persie.

If Arsenal had equalised, and the new talisman Adnan Januzaj remained kicking his elegant heels on the bench, the headlines would have been less effusive for Moyes. Instead he can reflect with pride on the contribution of Van Persie, the confident goalkeeping of David de Gea and particularly the displays of three England internationals. Rooney had the first touch of the game and was rarely far from the ball thereafter. United's No10 was deservedly named man of the match for his non-stop running, constant closing down of yellow shirts and creativity, including the corner for Van Persie's goal.

Phil Jones was immense, first in midfield, and then in defence when Vidic departed. Chris Smalling made some important interceptions late on. It made positive viewing for Roy Hodgson and Ray Lewington, as did Jack Wilshere's energetic late cameo for Arsenal, but they will be disappointed to lose Danny Welbeck (knee) and Michael Carrick (Achilles) for the forthcoming friendlies against Chile and Germany. Smalling's childhood love, Arsenal, departed vanquished and frustrated but they should not linger excessively on events here.

A first away defeat since March 3 in all competitions, and a record of never winning the title in a year when they have lost at Old Trafford, should not be allowed to trigger too dispiriting a debriefing when Wenger is reunited with his players after the international break. It was still strange to hear Wenger talk openly about his players being "too nervous", partly because they had not won here since 2006. He should be strengthening his players' mettle. Some had more than butterflies in their stomach.

Mikel Arteta played despite having been afflicted by the sickness sweeping the camp. Tomas Rosicky was feeling so poorly that he was sent home. Most significantly, Arsenal's defending at the decisive set-piece would have been more commanding had Per Mertesacker not succumbed to the bug. Thomas Vermaelen, the club captain, stepped up and, as Rooney pointed out afterwards, is hardly a shabby understudy. But Mertesacker's understanding with Laurent Koscielny has been so important this year.

In a side not known for its height, the towering Mertesacker was even more missed. Arsenal also lacked the pace to get behind United's back-line. Without Theo Walcott and Alex Oxlade-Chamberlain they are not a side blessed with great speed, barring the runs of Bacary Sagna and Kieran Gibbs from full-back (or Koscielny breaking forward). Arguably, their best performer was Sagna, who kept hoisting in some promising crosses. De Gea dealt well under pressure but once again Arsenal fans watching from the corner were reminded of the need to reinforce their attacking options.

Olivier Giroud has been magnificent this season but needed assistance superior to Nicklas Bendtner, whose continued employment by Arsenal is one of the more mystifying elements of the modern era. Arsenal's cutting edge was blunted by United's organisation, blocking and work-rate. The only manager to stop them scoring since February was Moyes with Everton. His United players were up for this. In the first half, Jones sat in front of the back-four, occasionally charging upfield, but otherwise looking to block the supply to Giroud. In the first half, Jones was a model of mature midfield play, not wasting any of his 13 passes and making three interceptions.

Arsenal had a similar sentry in Mathieu Flamini, who was occupied fully with Rooney, who saw a shot deflected wide, then whipped in a right-footed corner that David Beckham would have been proud of. Arsenal's zonal marking system was exposed badly. Nobody reacted to the run of Van Persie, who was already rising when finally challenged and his header flew past Wojciech Szczesny. The game became scrappy towards the break, interrupted by accidents. Jones challenged Szczesny fairly for an aerial ball, caught the keeper and looked bemused when booked by Michael Oliver.

Given Andre Villas-Boas' poor handling of Hugo Lloris' concussion, Arsenal were quick to point out their keeper "did not have any concussion" only "a whack on the bridge of the nose and watery eyes".

De Gea then collided with Vidic, who eventually climbed to his feet, slightly groggily, spitting blood from his mouth, waving away the stretcher. He was helped towards the tunnel, eventually to hospital. Jones took over at centre-half, brilliantly reading Mesut Ozil's pass to Santi Cazorla and then spiriting the ball round Aaron Ramsey. Smalling made a series of clearances, De Gea saved from Gibbs, Bendtner failed to connect with a Sagna cross before that final whistle came and Van Persie celebrated again.